The present invention relates generally to the field of flexographic printing and, more particularly, to a portable flexographic ink proofing apparatus for providing proofs of ink samples.
In the field of flexographic printing ink samples are obtained by drawing ink over a substrate using a hand ink proofer of the type manufactured by Harper Companies International of Charlotte, N.C. The ink is applied to the substrate by manually rolling the hand proofer across the substrate. Manual ink proofer tools are utilized for proofing ink colors in order to accurately predict the results to be obtained by running a selected ink specimen in a printing press. A computer microscope is then used to view the ink smear on the substrate. The computer then indicates to the operator various color components to be added to the ink in order to achieve the desired ink coloration.
In a flexographic printing operation, rubber plates are utilized for delivering the ink to the stock or paper to be printed. A flexographic ink technician is usually given an ink specimen which has been determined to be acceptable for use on a particular press, and a production run sample, to be used as the standard for color and density. One of the most difficult tasks facing a flexographic ink technician is proofing an ink in a manner so that the color will duplicate the color of the production run sample from the flexographic printing press. It is well known among those skilled in the art that if three trained technicians pull an ink proof, using the same ink on the same hand proofer tool, three different color shades will result.
Color shade on a flexographic printing press is dependent on the ink film thickness applied to the substrate or stock. The ink film thickness is determined by the speed of the press, the pressure applied between the printing plate and paper (i.e., impression), and the pressure between the rollers on the printing unit. Similarly, color shade on a flexographic hand proofer tool is also dependent on the ink film thickness applied to the substrate which thickness is determined by the speed at which the technician pulls the hand proofer across the substrate, and the impression pressure the technician applies to the hand proofer while moving it across the substrate. Thus, the speed and impression is totally dependent on the manual skill of the flexographic ink technician, while the only variable not controlled by the technician is the pressure between the ink roller and transfer roller of the manual proofer tool.
Accordingly, there is a need for an ink proofer arrangement that provides a reliable, consistent and repeatable ink proof on a substrate, irrespective of the experience of the ink technician producing the ink proof. An approach that addresses the aforementioned problems, as well as other related problems, is therefore desirable.
The ink proofer of the present invention substantially meets the aforementioned needs of the industry. According to one aspect of the invention, the ink proofer arrangement provides for the constant speed roller which feeds paper through the device at a constant speed to generate a uniform ink smear. Further, the ink proofer arrangement provides for regulated pressure between the roller and an underlying drum on which the roller bears. Additionally, in one example embodiment, the ink proofer arrangement is explosion proof being an all pneumatic device.
According to another aspect of the present invention, the ink proofer arrangement includes a rotating drum that is disposed opposite and beneath a proofer roll of a hand ink proofer tool. The proofer roll of the proofer tool is elevated above the rotating drum and is lowered into compressive rotatable engagement with the rotating drum when the substrate (preferably paper) is introduced between the drum and the roller. The substrate advances between the roller and the drum at a selected speed. The pressure of the roller acting on the drum is selectable by an operator. Prior to the substrate paying out, a sensor senses the imminent end of the substrate and raises the roller to prevent contamination by being in contact with the drum when no substrate is present.
According to another aspect of the present invention, a digital speed control and an adjustable print pressure mechanism are provided such that the speed, impression and roller pressure are completely controlled by the ink proof technician, whereby the same ink color will be duplicated each time the apparatus is used.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures in the detailed description that follow more particularly exemplify these embodiments.